Liquid and powder laundry detergent products for laundering of fabrics are known. A problem with these known forms of laundry detergent products is that consumers are required to measure out appropriate amounts of the detergent from containers, which often leads to consumers using too much, or too little detergent. Furthermore, the process of measuring out the liquid or powder detergents is inconvenient, and messy, often leading to accidental spills. Additionally, conventional powder and liquid laundry detergents are bulky and to deliver enough washing loads in a single package can require large and awkward containers which increases the costs of shipping and storing the products through the supply chain. As well these large containers can be hard for consumers to handle store and use.
Attempts to overcome the problems associated with the liquid and powder detergent products have led to the development of products containing pre-measured amounts of detergent in single use dosage forms, such as dissolvable laundry pouches containing, for example, liquid detergent (and often other cleaning aids), and laundry detergent sheets.
Dissolvable laundry detergent pouches filled with powdered and/or liquid laundry detergents are well known. These types of laundry detergent pouches have some perceived disadvantages however. First, the transfer of the detergent through the laundry pouch walls is not always sufficiently fast to deliver a full cleaning dose in the appropriate part of the laundry cycle. Second there are limits to the amount of laundry detergent that can be contained in a single pouch. Third, laundry detergent pouches are not configured to be split into smaller portions for use with smaller laundry loads. Fourth, laundry detergent pouches are generally bulky and large which increases their shipping and storing costs.
In contrast to laundry detergent pouches, impregnated laundry detergent sheets have a relatively small footprint, resulting in substantially lower shipping and storage costs throughout the supply chain. Their small physical dimensions also makes impregnated laundry detergent sheets eco-friendly since far less carbon is generated from fossil fuel energy spent in transporting them from their place of manufacture to the ultimate consumer, as compared to their bulkier liquid, powder, and pouch counterparts.
Known examples of impregnated laundry detergent sheets feature a substrate with a plurality of uniformly distributed perforations, into which is disposed a detergent composition. Passage of water through the perforations during the laundry cycle in a washing machine then aids in the release of the detergent to the substrate surface and into the wash water. In U.S. Pat. No. 4,853,142, a plastic web forms the substrate which supports the detergent in a sheet-like format. Similarly, U.S. Pat. No. 4,938,888 discloses a detergent combination impregnated into a flexible substrate composed of foam, foil, paper, and woven or non-woven cloth of various materials. A problem with these types of impregnated laundry detergent sheets is that the substrate does not dissolve in the wash water and remains in the washing machine after completion of the laundry cycle. These non-dissolvable substrates also tend to cling to certain areas of the clothing being washed, making it more difficult for the embedded detergent to release from the substrate completely.
U.S. Pat. Nos. 6,818,606 and 7,094,744, disclose attempts to overcome the above problems associated with laundry detergent sheets by using dissolvable substrates. The '606 patent discloses a sheet of laundry detergent comprising a layer containing a detergent composition and a water-soluble substrate provided on both sides of the layer, wherein the layer comprises a water-soluble or disintegrating-M-water particle group, having an average particle diameter of 60 to 2000 μm, consisting of a particle group. The '744 patent discloses a method for producing a sheet type laundry detergent in which a thin layer of a doughy detergent composition can be formed with uniform thickness and width while retaining high solubility and detergency on use. According to the disclosed method a doughy detergent composition is continuously or discontinuously applied onto a water-soluble or water-dispersable flexible support of continuous length that is running continuously in a prescribed direction to form a thin layer on the doughy detergent composition.
The use of a water-soluble or water-dispersable support eliminates the problems associated with an imperfect release from the substrate (i.e. a sheet of plastic or cloth), as well as problems of the substrate remaining with the clothes in the automatic washing machine at the end of the laundry cycle. However, the methods of making the laundry detergent sheets described in the '606 and '744 patents are complex. For example, the '606 patent teaches forming the substrate and detergent layers separately first. The detergent layer material is then sandwiched between two sheets of laminated water-soluble substrates and then heat sealed around the edges. The '744 patent similarly requires the water-soluble or dispersable flexible support to be formed first, then in a separate step, the doughy detergent composition is applied onto the water-soluble or dispersable flexible support.
Other prior art patent publications of general interest in the field of laundry detergent sheets include:                U.S. Pat. No. 2,112,963;        U.S. Pat. No. 2,665,528;        U.S. Pat. No. 3,694,364;        U.S. Pat. No. 3,904,543;        U.S. Pat. No. 3,950,277;        U.S. Pat. No. 5,574,179;        U.S. Pat. No. 6,864,196        U.S. Pat. No. 6,949,498;        U.S. Pat. App. Pub. No. 2008/0014393;        U.S. Pat. App. Pub. No. 2008/0064618;        U.S. Pat. App. Pub. No. 2009/0291282;        U.S. Pat. App. Pub. No. 2011/0136719;        PCT Int'l Pat. App. Pub. No. WO 2004/087857;        PCT Int'l Pat. App. Pub. No. WO 2006/134657;        PCT Int'l Pat. App. Pub. No. WO 2007/034471;        CA Pat. App. No. 2,695,068; and        EPO Pat. App. Pub. No. 2,226,379.        